Our primary intent is to understand the DNA inversion system (gin) of bacteriophage Mu. A 3000 nucleotide pair region known as the G-segment is bordered by inverted repetitious sequences at which intramolecular recombination occurs to invert the G DNA segment. We have mapped the trans-acting gin system necessary for the inversion within the beta region adjacent to the G-segment. We wish 1. to determine and map other components of the G-inversion system; 2. to carry out fine structure mapping of known functions in the G-segment and to identify new ones; 3. to identify the gin protein; 4. to sequence the boundaries of the G-segments of Mu and Pl phages. We have recently sequenced the Mu ends and shown than a mini-Mu segment consisting of both ends of Mu in a recombinant plasmid pTM2 can translocate. We therefore will also try 5. to study Mu and mini-Mu translocation during replication of infecting phages and induced lysogens.